1. Field of the Invention
The present invention relates to a circuit for supplying the transmission oscillator voltage for a piezoelectric sound source transducer.
2. Description of the Prior Art
It is known in the art to transmit ultrasonic waves generated by electrical excitation with an ultrasonic source transducer, to receive the echo signals with a sound pick-up transducer and to evaluate the electrical echo signals thereby obtained, for example, for range finding. As a rule, a transducer having a noticeable resonance step-up is employed in order to increase the acoustic power and the sound source transducer consisting of an oscillator having a low internal impedance is voltage-fed to its series resonance frequency EQU f.sub.o =1/2.pi.(L.sub.m .multidot.C.sub.m).sup.1/2,
wherein L.sub.m and C.sub.m are mechanical inductance and the mechanical capacitance of the equivalent circuit of the transducer.
Reception is executed with the assistance of a second, separate receiver transducer whose parallel resonance is provided by EQU f.sub.p =1/2.pi.{L.sub.m .multidot.(C.sub.m .multidot.C.sub.o)/(C.sub.m +C.sub.o)}.sup.1/2
where C.sub.o is the electrical parallel capacitance of the transducer in its equivalent circuit. The receiver transducer is high-resistant for the parallel resonant frequency f.sub.p and supplies a signal voltage from the received echoes which can be evaluated with a correspondingly great signal-to-noise ratio. Both transducers are matched in such a manner that F.sub.o of the transmission transducer equals f.sub.p of the receiving transducer. The fact that the frequency f.sub.o of a transducer is smaller than the frequency f.sub.p forces the employment of two transducers which are differently tuned, i.e. to different series resonant frequencies f.sub.o (of the transmission transducer) and f'.sub.o (of the receiving transducer).
Although it is at least conceviable, while accepting lower signal-to-noise ratios and/or lower receiving power, to employ one and the same acoustic transducer for transmitting and for receiving, particularly when the receiving transducer also has a very poor oscillatory quality, i.e., a very great band width (with a correspondingly small resonant step-up), another possibility is to work with only a single transducer and, while foregoing and effective electrical excitation and acoustic emission, to excite the transducer as a transmitter in the parallel resonant frequency f.sub.p.